1. Field of the Invention
The present patent application relates to a backflow-preventer for sanitary devices, especially sanitary fittings.
2. Discussion of the Background
Backflow-preventers or check valves are used in sanitary devices to prevent water from flowing back into a feed line whenever, due to pipe fracture for example, underpressure occurs in said feed line. In sanitary fittings having hose sprinklers, in particular, there is the danger of dirty water being sucked back into the feed line whenever, while the control cartridge of the fitting is open, the sprinkler head is immersed in the dirty water.
Generally, in the sanitary fittings field, commonly known disk valves are used as backflow-preventers. A valve disk is herein forced by means of a spring against a valve seat, so that they close sealtight even under very small return-flow pressures. Due to the axial movement of the valve disks, the guides begin to wear away over time, which can result in the disk valves no longer forming a seal. A further problem with disk valves consists of the fact that, whenever there is an intrusion of foreign bodies, the leakage can be considerable. If a grain of sand gets stuck between the valve disk and the valve seat, for example, a considerable flow cross section may remain clear.
Ball valves, too, are used as backflow-preventers. These valves, which can be produced at little cost, suffer virtually no wear and, having light balls, are quick to react. Where there is disturbance by foreign bodies, the same problems arise, however, as in disk valves. Since the balls are not spring-loaded, they exhibit erratic behavior, however, under small return-flow pressures.
In addition, the use of duckbill valves is also known. These exhibit a cup-shaped or hollow, wedge-shaped valve body made from elastomeric material, which valve body is held in a housing. The wedge-shaped valve bodies exhibit, at the pointed end, a straight slot, which connects the interior of the valve body to the environment. That wall of the valve body which limits the slot thus forms sealing lips. The cup-like valve bodies exhibit, in the region of the base, a rectilinear slot, which is limited by sealing lips which project outwards and are formed onto the base. If overpressure exists in the interior of the valve bodies, the slots open and the water is able to flow out through them. If underpressure exists in the interior, however, the sealing lips are pressed against one another by the higher ambient pressure and prevent any return flow. These valves exhibit virtually no wear, have low production costs, and still have relatively good closing characteristics if foreign bodies have intruded into the slot, since the thin sealing lips hug closely to them. A drawback, however, is that the sealing lips only come to bear fully against one another when there is a relatively high backwash pressure, with the result that they display erratic behavior under very small backwash pressures.
From U.S. Pat. Nos. 2,270,737 and 2,382,427, backflow-protection devices are known, which prevent water from being sucked back out of toilet bowls into the feed line by the fact that, in the event of underpressure on the side of the feedwater line, the rinse line is simultaneously ventilated and the back-suction of water is prevented by a check valve-like part. Inserted in the conduit of a tubular housing there is an outer sleeve, which is fastened to the housing by its end region on the inlet-side and is radially supported by means of an inner flange. Downstream of the inner flange, the outer sleeve exhibits a middle cylindrical section, which is adjoined by a widening end section. In the region of the middle section, the housing is provided with radial conduits, which are connected to the ambient air. Downstream of these conduits, the housing exhibits a further inner flange, which, together with the outer sleeve, limits an annular ventilation gap and whose end face facing away from the conduits is conically configured. A bell-like inner sleeve is located within the outer sleeve and bears with its free end region, at a distance from the free end of the outer sleeve, against the end section of the latter. When water flows through, the outer sleeve expands and comes to bear with its end section against the end face of the further inner flange, so as to close the ventilation gap. The escape of water through the conduits is thereby prevented. Under the pressure of the water, the inner sleeve bends inward, creating folds.
In the event of underpressure on the feed side, the outer sleeve is bent inward, so that its end section comes to bear snugly against the inner sleeve in order to prevent water from flowing back. At the same time, the ventilation gap is clear in order to ventilate the outlet. Since thin-walled, bell-like sleeves, when they bend inward, necessarily form wave-like folds or buckles, a subsequent, clean bearing contact against the outer sleeve is only guaranteed provided its inner contacting surface of the end section is correspondingly matched to the outer contour of the inner sleeve interacting therewith. In other words, the outer sleeve may bear against the inner sleeve with no or only extremely low pretensioning. This can result in the valve no longer being guaranteed to close cleanly under low return-flow pressures.